“Early guitar amps were often designed for use with accordions, steels, and microphones,” says Neil. “The first British model I saw was in 1947 – the Vortexion EG / 10, which was advertised in Wireless World as the ‘AC / DC amplifier’. Guitar amp valves typically provide amplification (preamp valves), power (power valves), and rectification.
“In the UK we often refer to a 12AX7 ECC83 dual triode preamp valve after the Philips / Mullard designation. Another well-known preamp valve would be the British Mullard EF86 pentode which you will find in some classic Vox models. Common power valves include the EL84 and EL34, which are original Philips / Mullard, and the American 6L6 and 6V6 found in Fender amps.
“Rectifier valves, such as GZ34, EZ81, 5Y3 and 5U4GB, etc., convert utility power to DC voltage. If the amp were to run on AC only, it would buzz loudly at 50 or 60Hz. It is also known as the “rectum fryer” because things are wrong and it is! When you strike the strings and pull energy from the rectifier, the voltage of the entire system drops momentarily. People love that sag and squeeze – the way the amp crashes and then pops out a bit. ”
1.ECC83 / 12AX7
“The rectifier is a diode, which means it has two parts (‘di’) and a three-part triode (‘tri’). A triode is the simplest amplifying valve there is, and a twin triode such as an ECC83 / 12AX7 is actually two valves in one. The 12AX7s have become the norm, perhaps because so many amp designs are historically based around them. I think one of the reasons we like the particular tones is that we’re used to them; we identify these sounds as “correct”. However, there is room for experimentation.
“For a different sound, you can normally swap the valve types in ‘family 12’ without any problem because the designs are self-biased. A lower gain 12AU7 or a 12AY7 can be an interesting alternative to a 12AX7, for example. Personally, I sometimes prefer these low gain preamp tubes because I find that pushing the output stage of the amp further creates a more complex sound.
“The EL34 [pentode] valve is legendary for powering classic British amps like Marshall, Hiwatt and Orange. Most people would say the EL34 has good bite, good crunch, and deep mids. They can produce a lot of power, and once the UK guitar world moved on to them, it stayed that way. As the amps got louder, they went from simpler auto-bias / cathode-biased designs to fixed-bias because that way you get so much more power. With a fixed polarization design, you will need to have the polarization checked / adjusted when you replace the valves.
“Compared to preamp valve distortion, power valve distortion can be very complex with more harmonics and harmonics, and you also get this nice volume compression when you pump the power. And when you stand near a big cab, you get all that interaction with the guitar. You can’t beat him.
“EL84 [pentode] valves are usually found in classic Vox amps. Besides being smaller and less powerful than the EL34, the EL84 produces several times more distortion and therefore sounds different. It’s not the best on paper, but that’s a different story once you put it in the context of a guitar amp where it produces a lot of nice overtones. The “bell” sound you often hear about EL84s is the complexity of the added harmonics created by this distortion.
“I think there is some kind of inherent conditioning that makes complex sounds stimulate our brains. Whether it’s a guitar sound or the dawn chorus of birdsong, it’s these natural movements and intricacies that make it fascinating to us. If you just heard the simple signal from the guitar, it would sound boring. The rock and blues based guitar sounds have a particular focus on tonal shaping.
4.6L6 & 6V6
“6L6 and 6V6 [beam tetrode] Power tubes are associated with American amps, especially Fender. The KT66 [kinkless tetrode] The valve used in early Marshall JTM45 amps is similar to the 6L6, which makes sense as the design was derived from the Fender Bassman 5F6A circuit. The 6L6s are used in larger, more powerful Fender amps like the Twin Reverb and Dual Showman, and the less powerful 6V6s are used in smaller Fender amps like the Princeton and Deluxe.
“I have the impression that the sound is characterized by a lower concentration in the mids than the EL84 and EL34, and more by an emphasis in the highs and lows. They usually sound a lot cleaner too. There’s definitely more of a “smile curve” going on, but Fender then voiced the amps to sound that way overall. At first, the designers tried to avoid distortion because musicians also used the amps for lap steels and accordions.
- Disclaimer: Due to the high voltages present in most guitar amplifiers, Guitarist recommends consulting an experienced professional if you wish to make any investigations or modifications.